This invention relates to a pressure swing adsorption process for obtaining a hydrocarbon from a gaseous stream containing hydrocarbons and a small amount of oxygen.
DOS No. 3,035,255 discloses a process for obtaining or recovering hydrocarbons from a gaseous stream containing hydrocarbons and a carrier gas, wherein methane in particular is separated in a pressure swing adsorption installation from a methane-air mixture. In this system, essentially methane-free air is discharged from the outlet end of the adsorbers while enriched methane is obtained as a stream of desorbate during the regenerating phase of the adsorbers. This method is oriented toward the complete separation of all hydrocarbons, especially toward the complete separation of methane from a methane-air mixture. The adsorption process proposed for this purpose contains, as an essential process step, an air displacement step with readily adsorbable components, especially with the methane to be obtained as the product, subsequently to an adsorption phase. Such a displacement step, effected to adsorption pressure, i.e. the highest process pressure, is disadvantageous because recompression of the methane to adsorption pressure is required for this purpose.
The hydrocarbon concentration in the applications contemplated by DOS No. 3,035,255 is relatively low; methane concentrations are cited of between 1 and 40 vol-% in the raw gas. Since the additional component is to be air, oxygen concentrations of about 12-20 vol-% are encountered in the raw gas. With such a high oxygen content, however, there is very great danger of explosion of the mixture so that operation of such a plant appears to be hazardous.
Also when processing raw gases of a low oxygen content, there is the danger that localized oxygen concentrations may occur in the adsorption plant shifting the hydrocarbonoxygen mixture into the explosive range.